Axial pin tumbler locks are well-known in the art. However, they have had many disadvantages in terms of manufacturing cost and quality. Thus, while the use and design of axial pin tumbler locks is advantageous, it will be desirable to have a lock design having lower costs of manufacturing and construction.
Axial pin tumbler locks often suffer from the disadvantage of having large profiles. Since the axial pin tumblers in a typical lock are disposed within milled cylindrical holes in annular sleeves, the width of the annular sleeves must be sufficient to allow wall support around the entire circumference of these cylindrical holes. This leads to unnecessary thickness and bulkiness of the sleeves, and also causes them to have a greater outer diameter than would otherwise be necessary. The inner diameter must be smaller for the same reason. As a result, the central spindle of the lock must also have a smaller diameter, which means it will have less strength to endure both radial force and withdrawing force caused by tampering. It would thus be desirable to have annular sleeves with smaller thicknesses and smaller outer diameters so that the overall profile of the lock could be reduced, without losing security or performance.
The previously used design of axial pin tumbler locks has also been disadvantageous where die casting of the parts is generally used. Die casting has the nominal advantage of being less expensive than other metal forming techniques. However, the limitations in the die casting process allow only weaker alloys of metal to be used in such a process. As a result, the resulting components are weaker than they otherwise could be by virtue of other casting processes. Further, die casting does not allow for the most accurate tolerances. The ability to use other casting processes which would allow for harder parts and better tolerances would thus be desirable. Components with better tolerances in casting could be designed for tighter fit, and thus add to any reduction in overall profile of the lock. Die casting also does not allow parts to be cast with internal openings, as are required in conventional axial pin tumbler locks. As a result additional working of parts after casting is required. This leads to weakening of the components and significant added cost.
Axial pin tumbler locks also suffer from the disadvantage of being susceptible to uncoding of the pins by means of slippage of one of the annular sleeves with respect to the other when the lock is between the locked and unlocked positions. As will be discussed in further detail below, uncoding of an axial pin tumbler lock can occur when the sets of cylindrical holes on the respective annular sleeves are slightly misaligned when the key is withdrawn. Because of this misalignment, the tumbler pins do not extend beyond the plane separating the annular sleeves, and the annular sleeves are not locked in place so as to prevent relative rotational motion. In such a situation, the rotating cylindrical sleeve can rotate either direction to a misaligned position, thus allowing the tumbler pins to cross the plane between the sleeves, albeit into improper cylindrical holes. After this occurs, insertion of a properly-coded key does not cause the line of separation of the tumbler and driver pins to be co-planar with the separating plane between the sleeves. That is, insertion of the key does not unlock the lock. Such uncoding of axial pin tumbler locks is common, and requires full disassembly of the lock to correct. It would thus be desirable to have an axial pin tumbler lock which had provision for preventing such slippage.